As the power or energy consumption of components of the computer systems continuously increases, the power budgets of the computer systems become tighter. It is necessary to manage power or energy consumption of a computer system to pursue high-performance goals, such as high computing power, compactness, quietness, better battery performance, etc. For example, portable computer systems, such as laptop computers, have a limited battery output capability, e.g., charge capacity. Managing of the power consumption for a given battery output capability may increase the performance of the computer system and extend a battery life. Generally, the power management allows a computer system to monitor its own energy dissipation, and adjust its performance to satisfy, for example, thermal constraints or battery lifetime goals.
FIG. 1 illustrates a typical computer system 100 that uses a precise sensor 102 for power monitoring. As shown in FIG. 1, sensor 102 is connected in series with power source 101 and a load 103 (e.g., a processor) to accurately measure the current through load 103. Typically, precise sensor 102 is a resistor having a calibrated fixed resistance, or a Hall-effect device. Typically, sensor 102 is a resistor having a tolerance value not more than ±0.5%. This resistor is often referred to as a sense resistor. Voltmeter 104 measures the potential difference between points 105 and 106 across sensor 102. By measuring voltage Vsense between points 105 and 106 across sensor 102, the current Iload through load 103 that is connected in series with sensor 102 is determined. Thus, to accurately measure the power of a computer system, subsystem, component, or circuit, an additional component, such as sensor 102, is introduced. Sensor 102 adds an extra cost, and also occupies an extra space in computer system 100. Sensor 102 continuously operates in computer system 100 and therefore dissipates an additional power. The power Psense dissipated by sensor 102 is determined as follows:Psense=Iload2×Rsense   (1)
Further, sensor 102 produces an extra voltage drop Vsense between power source 101 and load 103. Thus, sensor 102 is not only intrusive to computer system 100, but also may disrupt the performance of computer system 100.
Additionally, to measure a larger current range, sensor 102 desirably has a large constant resistance, and a voltmeter 104 that is capable of reading small potential differences (e.g., microvolts and smaller), or a Hall-effect device is used. Sensor 102 having a large resistance drives up the power of computer system 100. On the other hand, voltmeters that are capable of reading the small voltages and Hall-effect devices are expensive.
Thus, the presence of sensor 102 negatively affects the performance and efficiency of the computer system 100 while increasing cost and board area.